In order to study the effect of the human immunodeficiency virus (HIV) tat gene on the expression of cellular genes, we have constructed lymphoid lines that expressed the tat gene. This was done by placing the tat gene and an adjacent HIV long terminal repeat (LTR) into the retroviral vector pGV1. The recombinant plasmid was transfected into psi2 cells to produce an ecotropic viral stock that was used to infect psiAM cells. Colonies of G418-resistant psiAM cells were isolated and assayed for the production of virus. Supernatants of those colonies with the highest virus production were used to infect cells of the human T-cell lymphoid line, H9. G418-resistant cell lines derived from H9 were found to contain tat activity as assayed by fusion with HeLa cells containing LTR and CAT sequences. Furthermore, they contained an LTR-tat message of the predicted size.